Comment 4 for bug 1441883

Done, now xdiagnose only triggers if an installed display manager is configured as default but couldn't start. This should fix your boot issue.

We won't fail graphical.target anymore if the only available dm was uninstalled, however, I do recommend you set then your default target to multi-user.target (case on a server system for instance).

The lightdm part would be interesting to ensure /e/X/d-d-m is empty, but not required.